[FR] Please add an instruction to download artifacts in other tasks

[abravalheri]

Description

Would it be possible to provide an YAML instruction that downloads a build artifact previously uploaded in another task?

Let's suppose for example that a build task exists and uploads the build output as an artifact, for example:

build_task:
  container:
    image: python:3.9
  install_script: pip install tox
  build_script: tox -e build
  dist_artifacts:
    path: dist/*   # e.g.: dist/project-0.42.tar.gz and dist/project-0.42-py3-none-any.whl

It would be nice if another follow-up task could download the build artifacts for tests without having to manually install a tool for downloading and extracting the artifacts:

.test_template: &test-template
  alias: test
  depends_on: [build]
  artifact_download:        # <---- Currently does not exist, it would be nice if it did
      task: build           # Not sure what is the best syntax/names/arguments here,
      name: dist            # that can be further discussed/changed ...
      path: dist/*
  test_script: >
    tox --installpkg dist/*.whl -e lint,typecheck,test

linux_task:
  matrix:
    - name: test (Linux - 3.7)
      container: {image: "python:3.7-bookworm"}
    - name: test (Linux - 3.10)
      container: {image: "python:3.10-bookworm"}
      skip: $BRANCH !=~ "^(main|master)$"
    - name: test (Linux - 3.12)
      container: {image: "python:3.12-bookworm"}
    - name: test (Linux - 3.13)
      container: {image: "python:3.13-rc-bookworm"}
  install_script:
    - python -m pip install --upgrade pip tox pipx
  <<: *test-template

mamba_task:
  name: test (Linux - mambaforge)
  container: {image: "condaforge/mambaforge"}
  install_script:  # Overwrite template
    - mamba install -y pip pipx tox
  <<: *test-template

macos_task:
  name: test (macOS - brew)
  macos_instance:
    image: ghcr.io/cirruslabs/macos-monterey-xcode
  env:
    PATH: "/opt/homebrew/opt/python/libexec/bin:${PATH}"
  brew_cache: {folder: "$HOME/Library/Caches/Homebrew"}
  install_script: brew install python tox pipx
  <<: *test-template

windows_task:
  name: test (Windows - 3.12.5)
  windows_container:
    image: "cirrusci/windowsservercore:2019"
    os_version: 2019
  env:
    CIRRUS_SHELL: bash
    PATH: /c/Python312:/c/Python312/Scripts:/c/tools:${PATH}
  install_script:
    - choco install -y --no-progress python3 --version=3.12.5 --params "/NoLockdown"
    - pip install --upgrade certifi
    - python -m pip install -U pip tox pipx
  <<: *test-template

Context

Currently it is possible to download artifacts manually, but that requires installing a couple of tools to:

• Download the archive
• Unpack/unzip the archive

Depending on the OS used for each task, you may need different tools to do that, and the installation methods also vary.
This makes it difficult to implement re-usable chunks of YAML and requires the developer to either write a bunch of conditionals or to verbosely handle each execution environment individually.

Having a YAML instruction that handles the download and the unpacking/unzipping of the artifact would facilitate that process and help to write more maintainable .cirrus.yaml files.

Anything Else

Please note that in the past, it would be possible to use the cache instructions to achieve something very similar to this. However since the change in the macOS host mentioned in #1291 (comment), that is no longer effective for a multi-platform CI.

I suppose it could be possible to re-use some part of the implementation of the cache instruction for this new instruction because they would be doing more or less the same thing (downloading from an URL and unziping/untaring the archive somewhere).